stinger390

I finally launched my boat today here in the chilly fall water of New England. I installed the thermostats that everyone on the site suggested and it was nice to see the water temp gauges move and steady at 140 degrees. Thanks for all the information to those who helped me with that.

My port engine is giving me some trouble which I am attributing to carb problems. It has a very rich idle and has been difficult to keep running at idle without cleaning it out every few minutes. It was running somewhat ok until a long no wake zone. After passing, I gave it some power and could not get any power above 2000 rpm. More throttle would reduce rpms and when I pulled it back some the rpms would steady at 2000 and hold. Occasionally it would surge to 2500 and then back down. No amount of cleaning it out would help.

I pulled in to a marina and went to work. I changed both remote fuel filters (no water noticed in either) changed spark plugs, cleaned the strainer to the carb (not dirty), checked distributor for moisture, loose wires etc, and re-set the 4 corner idle screws to Demon factory setting of 1 1/2 turns out. It started fine and idled smooth. I tried adjusting the float level again with no results noticed. Since it was running fine I figured I would try it out on the water under load. Gave it power and the port engine promptly died. I re-started and even in neutral with any power it would die out, although it is idling fine now. (although still noticable rich with fuel in the exhaust and some smoke.) Right engine has a slow bumpy and hesitant pickup to 1500 RPM but smooths out after that and runs great.

Where do I start from? Any base line settings I should go to with the float level adjustment, 4 corner screws, etc? Here are the specific related parts for your help with knowing whats going on:

Gen IV 454, 440 cyclone, BG Speed Demon 850 auto carbs with no choke and mechanical secondaries (pri - #85 sec - #83 jets), Thunderbolt IV ignition (new sensors), NGK BR6FS plugs, hurricane single plane high rise alum. intake, mild cam with no overlap, Holley 130GPH mechanical fuel pump with no pressure regulator.

Any suggestions on where I sould start? Fuel was high octane with an octane booster, but a few years old when I started(only 40 gal or so left over in the tank from the old motors, motors which I am wishing I kept now) I then filled with 150 gal of 93 octane about a month ago. (10% ethanol)

Thanks guys, pretty soon I hope to stop asking so many questions, but I guess thats how I am to learn something......

hillbilly24

If you ask me that gas has got to go. Put it in the truck or the lawn mower or something but get it out of the boat. 3 year old gas is way past done and month old 10% ethanol is actually passed it's prime too. Gas with Ethanol in is has about a 2 week shelf life and that's about it before it starts to degrade. If your not gona burn it within 2 weeks you need to put fuel stabalizer in it, I actually just recomend putting stabalizer in every time you fill up with todays gas blends. I can't say that it will run perfect with new fuel but there is no point in settign the carb up with that fuel running through it, if you get it to run right it will be all wrong when you get fresh fuel in it anyway.

stinger390

If it was the quality of the fuel causing my problem, would'nt the stbd engine be running terrible as well? They both draw from the same tank. There also was very little of the older fuel in the boat, that was stabalized and did not smell varnishy or even look old (when I removed and sampled 50 gallons into a clear 50 gallon container), and all opinions from those who saw the 50 that I removed said it looked, smelled, and felt fine and why was I removing it from the boat? I figured that what was left when mixed with new 93 would be ok. (this stuff is liquid gold these days right...)

The front sight gauge to the front fuel bowl is showing constantly full. I can't seem to get the level to adjust. I was thinking the needle and seat could be obstructed, or fuel pressure is too high for the needle to seat but would'nt that cause the fuel to run out of the carb? And, the stbd engine has the same fuel pump without a problem.

Everything seems to point to a very rich carb. fuel in the exhaust, dark smokey exhaust (especially when reved), the bogging out when power is advanced under load, black spark plugs (before I changed them). The standard plugs for this motor are BR6FS NGK's. Could a 6 be too cold for the higher power output and should I try a hotter plug? The Barry Grant site calls for a main jet size of 85 and sec of 93. I have 85 pri - 83 secondary which seems too lean. I know that should not come in to play until higher power is reached but could that jet discrepancy make any difference? I'm all confused at this point.

Todd

stinger390

Replaced a mangled main needle and seat assembaly today and cleaned carb metering blocks, bowls, etc. Got it running ok at the dock and idling up the river in gear Idled up to the end of the no wake with no problems, running great. (except for still a noticable fuel slick in the exhaust.) Gave her some power and she stopped at 2000 and would pulsate up and down between 2000 - 2200 RPM but no higher. Hard to keep it running after that and did not start very easily. Tied up on one engine. Noticed what looked like an amount of blue exhaust smoke, but I'm not positive. (sticking oil ring? bad compression?)

Pulled all 8 plugs and all were black and some wet with oil or fuel, or something. (replaced left bank yesterday, right bank a few days ago.) Replaced all 8 with new tonight but have not run yet as I wanted to check the initial timing in the morning.

This is how I have the carbs set as of now: primary and secondary floats at the middle line on the sight gauge, 4 corner screws 3/4 turn out (have tried several settings) I checked the float level when I had the bowl off and the float seated at .5" from the top of the bowl when I turned it upside down. Everything clean and no water or setiment anywhere in the filters or carbs. I'm thinking that blue smoke was not a mirage. 7 hours on motor, only .5 above 1500 rpm.

I'm running low on ideas here, except that I'm going to start shopping for oars pretty soon. It might go faster. Where should I keep looking, vacuum, carb, timing, ignition? Thunderbolt IV, how do you determine the timing advance on that system, and even if it is working?

Todd

MILD THUNDER

iTrader: (3)

I think you will really have to narrow it down to whether its a fuel, or ignition problem. Try swapping the carbs between the two motors. (assuming you have twins?) Make sure its firing on all 8 cylinders. Get some insulate pliers and remove the plug wires from the cap and see if the rpm's drop. If you remove a wire and no change, then you can focus on that cylinder. If you have cylinders not firing, it will cause the plugs to be wet and fouled. Since its a new motor, triple check the firing order. Many guys chase similiar problems only to find crossed plug wires. Stick a timing light on it and check the base timing and the advance. My cyclone 454's have a 0 mark and a 30 mark on the crank. Make sure base timing is checked on the zero mark. Run the engnine to 3000 and check the timing on the crank. How does it run in nuetral? Does it pop or backfire at all?

Pure Energy

Sound way rich. My 502's were jetted 78 primary. If you have a sheen on the water and wet plugs...I say too much fuel.

biginches

blue smoke might be all that fuel washing oil off the cyl walls.either way , way too much fuel is bad

MILD THUNDER

iTrader: (3)

My 420's are running holley 800's with 71p, 84s with a 6.5 PV in the rear.

stinger390

It seems like it does not want to start is slowly comes to life when cranking over, not a nice snap over like the stbd motor. Once running it does seem to pop a little especially when reved. I did see a few occasions when the engine would quit it would spit a mist of fuel like a back pop through the carb. Now, if it looks like it will stall I just hit the key off before it does to keep that back pop from happening. It does not seem to backfire aggressively, but certainly does not sound smooth, especially when reved.

I'm wondering of my Thunderbolt IV module is any good. I'm going to check my timing this morning, I think 8-10 degrees BTDC is right for this engine for base timing, but I'll check the book. If the module is bad I'm assuming I wont see the timing mark move when the engine is reved to 3000? If the module is good (V8-24) what should the timing mark move to, is it 24 degrees or more BTDC?

stinger390

Also, my carb is a BG speed demon 850 with 85 main jets, and 83 secondary. I have not checked the other carb for it's jet size, but since they are a matched pair of engines, together since new, I assume they are the same setup. Perhaps I should not assume. When do the jets take over from the idle circuit anyway? I thought they were for higher power running. I'm fairly sure my power valve is 6.5 as well.
One guy mentioned he thought my carbs were a little too small but I can't imagine they are on 454's with only mild mods. If anything I was thinking too big.